[Webkit-unassigned] [Bug 103727] New: Unset NodeMustGenerate flag for Call nodes of few String.prototype.* pure functions

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=103727

           Summary: Unset NodeMustGenerate flag for Call nodes of few
                    String.prototype.* pure functions
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: dm at ispras.ru


Function calls have NodeMustGenerate flag set, but this is redundant in case the function has no side effects.  This patch aims to remove NodeMustGenerate flag for Call nodes of String.replace, String.split, and String.indexOf, if their argument types imply no side effects. This would allow to eliminate such calls, if their result is unused.

Example:

function foo() {
  var str = "split it up";
  var i;
  for (i = 0; i < 10000; i++) {
    var x = str.split(" ");
  }
}

var i;
for (i = 0; i < 1000; i++)
  foo();

Run time w/o patch: 1.756s
With the patch: 0.032s

Is it, in general, the right way to eliminate redundant calls?
I admit that using strcmp is not the best way to check for function names -- probably it would be better to create a hashtable with mapping of function names to argument checking routines, but for now I just would like to get some feedback to know whether this optimization is correct and if the WebKit community is interested in it.

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